University of New Hampshire doctoral student Matt Wallhead (left) and assistant professor of plant pathology Kirk Broders with an unmanned aerial vehicle they're developing. Photo by Rachel Rohr.
Satellites are commonly used to monitor large-scale environmental changes, and airplanes are often used to get a clearer picture of the overall health of particular forests. Now, a plant pathologist at the University of New Hampshire is working to equip low-cost drones with the technology to detect diseases in individual trees before those diseases even become visible to the naked eye.
Kirk Broders is focusing his efforts on helping farmers detect apple scab, a fungal disease he says affects 100 percent of apple orchards in the Northeast. It causes dark scabs on the leaves and the skin of apples, and while it is harmless and has no effect on flavor, the blemishes render the apples unmarketable. So the disease is the top concern of conventional apple growers in the region, all of whom spray a fungicide on their crops eight to twelve times per year to fight it.
Broders is testing the use of remote-controlled aerial vehicles – he prefers not to call them drones, so as not to confuse them with models used by the military – equipped with infrared technology to assess orchards for signs of disease. “You and I see chlorophyll as green, but it can also be seen as red at different wavelengths,” he explained. “If a fungus has infected a leaf, it kills the cell and kills the chlorophyll, which the camera sees as an uneven reflectance. A healthy leaf reflects a bright bold red, but unhealthy leaves show a patchy image.”
Scouting orchards for signs of diseases and pests is a time-consuming task for orchard managers, but unmanned aerial vehicles could do the job quickly and easily. Daily surveillance could help farmers pinpoint problems, act in the early stage of an infection, and better target the use of pesticides.
“It would be great if each grower had their own aerial vehicle, but a more realistic goal is to get them into the hands of crop consultants who could routinely visit farms to conduct orchard assessments,” Broders said.
And it’s not just apple scab that could be detected. The UNH scientist said that small multispectral cameras mounted onto drones could potentially be used to detect water stress, nutrient deficiencies, and a wide variety of other problems. “We could map an entire forest in fine detail to determine the percent of trees that are affected,” he said. “Everything you can do with satellites and planes can now be done with unmanned aerial vehicles with higher resolution.”
Broders’ research is still several years from commercialization. He is currently working with different types of cameras to determine the optimal image resolution, and he is studying different computer programs that will process the images. The Federal Aviation Administration is another hurdle to implementation, since they require a certificate of authorization for the commercial use of drones. But given the pressure that various industries are placing on the agency, it won’t be long before drones are deployed in many settings – including over forests and orchards – on a regular basis.